1. Field of the Invention
The present invention relates to a valve operating system for an internal combustion engine, and more particularly, to a valve operating system in an internal combustion engine, which is designed so that the operational characteristic of an engine valve which is an intake valve or an exhaust valve, can be changed in accordance with the operational state of the engine.
2. Description of the Prior Art
A valve operating system in which the intake and exhaust valve characteristics can be changed is already known, for example, from Japanese Patent Publication No.7-107368 or the like.
The above known system is arranged, so that a rocker arm connected to the engine valve, is driven in an alternatively switched manner by a plurality of valve operating cams having different cam profiles, whereby the operational characteristic of the engine valve is switched between two or three stages, in accordance with the operational state of the engine. However, to further enhance the engine performance such as output torque from the engine, specific fuel consumption and exhaust gas properties, it is desirable that the operational characteristic of the engine valve be switched more finely in accordance with the operational state of the engine. In the arrangement of the above known valve operating system, a larger number of valve operating cams having different cam profiles are required, resulting in an increase in size of the valve operating system, and in difficulty to realize the valve operating system.
In addition, the above known valve operating system includes no means for detecting the lift state of the engine valve and hence, it is difficult to carry out feedback control of the engine valve and to detect an abnormality in the lifting of the engine valve.